When I input a whole note it automatically advances to next measure. I need to build a chord. How do I stop it from advancing on its own

https://musescore.org/en/node/275075#comment-847722?

Also, press and hold the Shift key to build a chord. See https://musescore.org/en/handbook/note-input#chords

To expand a bit on those answers:

• First, although the cursor advances, you can still still build chords using the keyboard shortcuts, Shift+letter. If you prefer clicking in the score to enter notes so you need to see the note you just entered, you can move the cursor back by pressing the left arrow.

• MuseScore obviously has no way of knowing if, after entering a note, you plan to add another note to the chord or move on to the next beat. So no matter which way it guesses, it's going to be right sometimes, wrong other times. Overall, it's more common to move on (chords, after all, are normally not used in music for instruments that can only play one note at a time), so that's what MuseScore does by default. But obviously, in music for piano or guitar, this may or may not be the case. While the cursor always moves forward, there are two things you can do to make life easier. One is to enter music in "Continuous View" instead of "Page View", so that even if the cursor moves forward, the previous measure will generally still be in view. The other is to turn off the "Pan score automatically" button. The cursor will still move on, but the score won't reposition.